Laminated core



Nov. 29, 1949 H. F. PORTER LAMINATED CORE Filed Dec. 3, 1946 2 Sheets-Sheet 2 Y gwumkom Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE LAMINATED CORE Harry F. Porter, Elkim Park, Pa.

Application December 3, 1946, Serial No. 713,628

The invention relates to the art of electromagnetic induction apparatus, and particularly to the manufacture of laminated cores for transformers and the like.

It is known that oriented silicon steel exhibits properties of high magnetic permeability and low hysteresis losses in the direction of its elongation from rolling. The value of this superiority in performance is particularly pronounced at rather high flux densities, permitting reduction in the size of power transformers where the cores are designed to make use of the highly directional magnetic superiority.

Various types of cores have been developed to accomplish this result, notably, wound cores and those made up of stamped laminations. It has been found that laminated cores are superior to wound cores because they are accurate as to dimension and all parts can be assembled totally free of mechanical strain or distortion. Further, the reluctance of the core joints can be reduced to very low values as compared to wound cores which are out after annealing in final shape. Such wound cores entail a double butt joint in the core path. Spirally wound cores develop final strains after assembly that increase the hysteresis losses and excitation voltamperes somewhat above the minimum values obtainable in stamped lamination cores properly fabricated and assembled. Stamped lamination cores have many advantages over wound cores, and particularly are their advantages definite and pronounced in the construction of fractional kva. transformers.

Prior to the advent of this invention, it has been the practice to stamp core laminations with the legs and end sections of the same width or cross sectional area. ,Oriented steel laminations so stamped present cross grain areas which are of lower permeability than those in which the magnetic flux parallels the direction of the grain. In consequence, the distribution of permeability as well as core loss throughout the length of the magnetic circuit has not been uniform.

An object of this invention is to provide a core lamination of oriented steel having a major por tion disposed in the direction of the best properties of the steel and a minor portion at 90 to the direction of rolling but proportioned so as to provide a uniform distribution of core loss and uniform magnetic reluctance throughout the length of the magnetic circuit. I

A further object is to provide an oriented steel core lamination wherein a major flux path lies in the direction of the best properties of the metal and a minimum flux path length of greater width than the major flux path extends transversely of the direction of the best properties of the metal.

with the foregoing and such other objects in view as will be. apparent to hose skilled in the art,

1 Claim. (Cl. -356) 2 combination, and arrangement of parts hereinafter described and claimed and illustrated in the accompanying drawings, in which:

Figure 1 is a plan view illustrating the manner of stamping out core laminations from a strip of rolled oriented steel;

Figure 2 is an elevation of an assembly of a core made up of laminations formed as in Figure 1, with a coil positioned thereon;

Figure 3 is a horizontal section taken through Figure 2.

Figure 4 is a view similar to Figure 1 but illustrating another structural embodiment of core laminations;

Figure 5 is an elevation of an assembly of laminations formed as in Figure 4, with a coil positioned thereon;

Figure 6 is a horizontal section taken through Figure 5;

Figure 7 is a plan view illustrating the manner of stamping still another form of core laminations; and

Figure 8 is a vertical section through an assembly oi laminations formed as in Figure 7, with coils mounted thereon.

In the practice of this invention, the core laminations are formed by stamping froma strip of rolled silicon steel. Elongation of the metal occurs in the rolling process and the grain is caused to lie in the direction of elongation. Magnetic permeability is highest in this direction and hysteresis loss is lowest. With reference to this directional advantage, the steel is oriented.

In the embodiment shown in Figures 1, 2 and 3, a thin strip of rolled silicon steel l0, advanced from left to right in Figure l, is subjected to a stamping operation for the successive severance of substantially U-shaped laminations ll having a pair of spaced parallel legs l2 of identical width and an integral bight portion iii. In iorming the legs l2, the strip of metal stamped from the blank l0 provides a bar I4 of rectangular shape elongated in the direction of the best properties of the steel. It is dimensioned in width to equal the width of a leg, and in length to equal the overall width of the lamination so that, as shown in Figure 3, it may be assembled with the ends ofthe .legs I2 to complete the nux path for the magnetic its major axis is perpendicular to the major axis of the lamlnation and is, therefore, transversely directed with respect to the grain direction of the steel. This cross-grain disposition of the portion l3 makes it inherently less permeable and higher in core loss than those portions such as the legs I! and end bar H which substantially parallel the direction of the best properties of the steel. Northe invention consists in the novel construction, 50 mally, if the width of the cross-grain portion l3 aeaaorv 3 were the same as that 01' the leg I! or the bar 14, the magneticreluctance and core loss would be higher in the portion it than in any other portion or the lamination. As a result, there would be an unequal distribution of magnetic reluctance and core loss over the extent oi the flux path.

This invention obviates such an undesirable condition by providing a wider flux path in those portions of the lamination where the flux path is required to fellow a course at right angles to the direction or best magnetic performance. In order to achieve this result, the portion I8 is made wider in the direction or its minor axis than the width of either leg I2 or the bar ll, so that it is wider than the space between the legs giving an increased cross section area oi metal with lower flux density and consequent reduction in magnetic reluctance to compensate ,tor the crossgrain lower permeability characteristics of the metal at that point.

The final assembly comprises a core formed of a requisite .number of superposed laminations with a coil i5 mounted on one bank or the legs 12, and with the laminations alternately reversed to dispose an equal number of portions i3 bars 16 at each end of the core.

In the embodiment shown in Figures 4, 5 and 6, the same principle is employed in the tormation oi E-type core lamination. The blank strip 66 of rolled silicon steel is stamped to provide two outer legs ll of equal width and a naiv center leg 18 or double the width of a single outer leg. One of the rectangular strips or metal is which is stamped irom the blank it in fo the legs provides an end bar for assembling at the leg ends to complete the path or the magnetic circuit. This bar has its longer dimension in the direction of the best magnetic properties of the metal, as also are the legs i1 and 18. The width 01' the bar is the same as that or an outer leg ii and its length equals the overall width of the ltion.

The vertical leg portion 20 of the E lamination extends transversely of the grain direction of the metal, which requires the flux path to be at right angles with respect to the direction of the best magnetic properties of the steel. In order to compensate for the lower permeability and higher core loss incident to cross grain flux travel, the

portion 20 is made wider in the direction of its minor axis than the width of either outer leg 11 or the bar 19. In consequence, it is wider than the space between adjacent legs.

In making up the final assembly of core and coil, the laminations are superposed in alternately reversed relation. The coil 2| is mounted on the center leg l8.

Figures 7 and 8 illustrate some construction wherein each lamination is in itself an integral closed magnetic circuit. In forming each lamination, a circular portion 22 of the desired overall size is stamped from a blank 23 of cold-rolled silicon steel having pronounced superiority of magnetic properties in the direction of rolling. .An elliptical center section is removed in the same operation, leaving an elliptical center opening 24. The necessary widening oi the flux path at those portions in which it traverses the direction of the best magnetic properties of the metal is obtained by disposing the minor axis 01' the elliptical aperture 24 parallel to the direction of the best properties of the metal. The coils II are mounted over the portions of lesser width. Alternatively to the lamination form shown in Figure 7, the center opening may be of circular shape and the exterior configuration may be elliptical.

All i'orms oi the invention embody the same principle of having a predominant portion of the core lamination extending in the direction of the 10 that portion in which the flux path flows across the metal grain being widened to the proper proportions to eil'ect a uniform magnetic reluctance and a uniform core loss over the entire extent oi the magnetic circuit.

It is to be understood that the invention is not restricted to the matter herein described and illustrated. It is intended that within the scope of the invention as claimed, changes and modifications oi structural details and arrangement or parts may be made as desired.

1 claim:

Electromagnetic induction apparatus comprising a core of superposed identical alternately reversed laminations of magnetic metal each consisting of an end portion, a pair of outer legs and a middle leg integral therewith and extending perpendicularly therefrom in parallel spaced k relation in the direction of the best magnetic properties of the metal, the spaces between said legs being equal as to width and length, all said legs being equal in length and the outer legs being equal in width, said end portion integral with the legs extending transversely of the direction of the best magnetic properties of the metal and being equal in length to the length of a leg and greater in width than the width of either outer leg and belt: also greater in width than the width of the space between adjacent legs, and a separate end piece abutting the free ends of said legs and of the same length and width as an outer leg, each said separate end piece having its major ams in the direction or the best magnetic properties of the metal and being less in width than said end portion. integral with the legs whereby, in association with the adjacent alternate wider end portions, the opposite ends of the core are corrugated for low excitation and cooling; and a winding 01 current conducting coils mounted on the bank of superposed middle legs of the core laminations.

HARRY F. PORTER.

REFERENCES CH1 The following references are of record in the file oi this patent:

UNITED STATES PAs OTHER REFERENCES High-Q iron-cored inductor calculations, Electronics, Aug. 1945, pages 119-123.

best magnetic properties of the metal, and with- 

